The present invention relates to a process for the production of polyolefine-based fibrids and to the fibrids obtained; these fibrids possess an excellent compatibility with cellulosic paper pulp and thus lead to the production, from mixtures of these fibrids with cellulosic pulp, of mixed papers having improved characteristics. Moreover, these fibrids are easily suspended in water. Thus, they can easily be processed by the conventional papermaking techniques.
Various processes are known which permit the direct production of polyolefine fibrids which are compatible with cellulosic pulp and which can easily be suspended in water, these processes involving the known technique of the abrupt expansion of a solution of molten polymer by passing it through a suitable orifice.
Thus, Belgian Pat. No. 824,531, filed on Jan. 20, 1975 in the name of Solvay and Cie., proposes to produce this type of fibrid by subjecting, to abrupt expansion, a solution containing a polyolefine, which has been subjected to a prior oxidation treatment, and a polar monomer which can be grafted onto the polyolefine. This process involves carrying out two successive steps, which complicates the process and increases the cost price of the fibrids.
In order to avoid resorting to a process involving two successive steps, Belgian Pat. No. 847,491, filed on Oct. 21, 1976 in the name of Solvay and Cie., proposes to incorporate, in the molten polymer/solvent mixture subjected to the abrupt expansion, a polar monomer which can be grafted onto the polymer used, and to cause the grafting onto the polymer before the abrupt expansion. However, this process exhibits another serious disadvantage. In fact, a secondary reaction in which the polar monomer is grafted onto the solvent causes the formation of oligomers, consisting of grafted solvent, which are subsequently found in the water in which the fibrids produced are suspended, and the hydrolysis of which leads to corrosive products. This reaction obviously also causes the loss of some of the polar monomer and some of the solvent.
The known processes also exhibit a common disadvantage, namely that the grafted polyolefine is grafted throughout its bulk, whereas, in order to ensure an adequate compatibility between the polyolefine fibrids and the cellulosic pulp and the ease of suspending the fibrids in water, it suffices for the fibrids to be grafted on their surface. The known processes thus involve the use of a large excess of polar monomer, relative to the amount which is actually necessary.